s390x/css: provide a dev_path for css devices

We need to implement the get_dev_path method for the css bus, or
else we might end up with two different devices having the same
qdev_path.

This was noticed when adding two scsi_hd controllers: The SCSIBus
code will produce a non-unique dev_path for vmstate usage if the
parent bus does not provide the get_dev_path method.

We simply use the device's bus id, as this is unique and we won't
have any deeper hierarchy from a channel subsystem perspective
anyway.

Note that we need to disable this for older machine versions,
as this changes the migration format.

Reported-by: Marc Hartmayer <mhartmay@linux.vnet.ibm.com>
Reviewed-by: Halil Pasic <pasic@linux.vnet.ibm.com>
Reviewed-by: Sascha Silbe <silbe@linux.vnet.ibm.com>
Tested-by: Marc Hartmayer <mhartmay@linux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>

hw/s390x/css-bridge.c

@@ -59,11 +59,28 @@ static void virtual_css_bus_reset(BusState *qbus)
     css_reset();
 }
 
+static char *virtual_css_bus_get_dev_path(DeviceState *dev)
+{
+    CcwDevice *ccw_dev = CCW_DEVICE(dev);
+    SubchDev *sch = ccw_dev->sch;
+    VirtualCssBridge *bridge =
+        VIRTUAL_CSS_BRIDGE(qdev_get_parent_bus(dev)->parent);
+
+    /*
+     * We can't provide a dev path for backward compatibility on
+     * older machines, as it is visible in the migration stream.
+     */
+    return bridge->css_dev_path ?
+        g_strdup_printf("/%02x.%1x.%04x", sch->cssid, sch->ssid, sch->devno) :
+        NULL;
+}
+
 static void virtual_css_bus_class_init(ObjectClass *klass, void *data)
 {
     BusClass *k = BUS_CLASS(klass);
 
     k->reset = virtual_css_bus_reset;
+    k->get_dev_path = virtual_css_bus_get_dev_path;
 }
 
 static const TypeInfo virtual_css_bus_info = {
@@ -95,6 +112,12 @@ VirtualCssBus *virtual_css_bus_init(void)
 
 /***************** Virtual-css Bus Bridge Device ********************/
 
+static Property virtual_css_bridge_properties[] = {
+    DEFINE_PROP_BOOL("css_dev_path", VirtualCssBridge, css_dev_path,
+                     true),
+    DEFINE_PROP_END_OF_LIST(),
+};
+
 static void virtual_css_bridge_class_init(ObjectClass *klass, void *data)
 {
     HotplugHandlerClass *hc = HOTPLUG_HANDLER_CLASS(klass);
@@ -102,12 +125,13 @@ static void virtual_css_bridge_class_init(ObjectClass *klass, void *data)
 
     hc->unplug = ccw_device_unplug;
     set_bit(DEVICE_CATEGORY_BRIDGE, dc->categories);
+    dc->props = virtual_css_bridge_properties;
 }
 
 static const TypeInfo virtual_css_bridge_info = {
     .name          = TYPE_VIRTUAL_CSS_BRIDGE,
     .parent        = TYPE_SYS_BUS_DEVICE,
-    .instance_size = sizeof(SysBusDevice),
+    .instance_size = sizeof(VirtualCssBridge),
     .class_init    = virtual_css_bridge_class_init,
     .interfaces = (InterfaceInfo[]) {
         { TYPE_HOTPLUG_HANDLER },

hw/s390x/s390-virtio-ccw.c

@@ -322,6 +322,10 @@ static const TypeInfo ccw_machine_info = {
             .driver   = TYPE_S390_IPL,\
             .property = "iplbext_migration",\
             .value    = "off",\
+        }, {\
+            .driver   = TYPE_VIRTUAL_CSS_BRIDGE,\
+            .property = "css_dev_path",\
+            .value    = "off",\
         },
 
 #define CCW_COMPAT_2_5 \

include/hw/s390x/css-bridge.h

@@ -16,7 +16,14 @@
 #include "hw/qdev-core.h"
 
 /* virtual css bridge */
+typedef struct VirtualCssBridge {
+    SysBusDevice sysbus_dev;
+    bool css_dev_path;
+} VirtualCssBridge;
+
 #define TYPE_VIRTUAL_CSS_BRIDGE "virtual-css-bridge"
+#define VIRTUAL_CSS_BRIDGE(obj) \
+    OBJECT_CHECK(VirtualCssBridge, (obj), TYPE_VIRTUAL_CSS_BRIDGE)
 
 /* virtual css bus type */
 typedef struct VirtualCssBus {